The present invention relates to a method of forming end pieces on plastic molding strips. The molding strips have at least one hollow chamber which extends lengthwise in the molding. The end pieces are formed, by injection molding, on the ends of the molding strip in a plastic injection mold which is shaped to receive the end regions of the molding strips. The openings into the hollow chamber of the strip is covered in the mold to prevent molding compound for entering into the chamber.
The invention furthermore relates to an apparatus for carrying out the method of the invention. The apparatus includes an injection mold having two mold halves between which there is defined a clamping space for receiving and clamping an end of the molding strip and a mold cavity into which molding compound is injected to mold an end piece onto a free end of the strip.
Plastic molding strips are used frequently in connection with vehicles. They can have ornamental and protective functions. Plastic molding strips are produced by extrusion and are generally provided at both ends with a respective end piece. This is particularly the case in the molding strips to which the present invention relates and which is characterized by its hollow chamber which extends in the longitudinal direction of the molding.
It is known, for instance, from Federal Republic of Germany Application DE-OS No. 17 55 596 and DE-OS No. 19 50 412 to produce end pieces separately by injection molding and to thereafter attach them to the molding strips by bonding, welding, clipping, bolting, etc. The foregoing method is, however, very expensive because of the additional production steps and, further, its appearance is not optimal because of visible separation seams. Federal Republic of Germany Application DE-OS No. 17 55 596 suggests the possibility of injecting end pieces directly on the end of the molding strips. However, the suggestion is made with respect to solid molding strips not having a continuous hollow chamber within. The method could not be used universally because pressurized molding compound would enter the strip.
To overcome this problem, plugs having end collars are produced in a separate injection molding process. The plugs are inserted into the ends of the hollow chamber of the molding strips and then the actual end pieces are injection molded onto the ends of the molding strips within an injection mold which receives the end regions of the molding strips. This manufacturing method is disadvantageous in several respects. First, a separate manufacture and mounting of the plugs is required resulting in added costs. Furthermore, the collar of the plugs which rests against the end of the molding strip is not sufficiently supported, particularly if the molding strip is made with a relatively thin wall. Moreover, the presence of the collar reduces the contact surface between the ends of the molding strip and the end pieces, resulting in a poor connection. Another significant disadvantage of the conventional method is that the full injection pressure acts both on the plug and on the end surface region of the molding strip when end pieces are formed by injection molding. The injection pressure must, however, be kept within a very limited range in view of the fact that axial displacement of the molding strips during the injection process is not permitted and further because the hollow molding strip cannot be clamped in position with a large force. This means that the end pieces do not assume the surface structure of the mold cavity so that the gloss or finish of the molding strip and the end pieces differ. The end pieces are generally shinier than the duller looking molding strips, which is undesirable.